132 INNERVATION. [CHAP. XXI. 



tion which is chiefly developed.* In the cyclostomatous fishes the sympa- 

 thetic is said to be wholly deficient. 



For the sake of description, the sympathetic in the human body 

 may be divided into the following portions, 1. The Cephalic. 2. The 

 Cervical. 3. The Dorsal. 4. The Lumbar. 5. The Sacral. 



In comparing these several portions, we find that they have cer- 

 tain characters in common. Each portion consists of its proper 

 number of ganglia, which seems in some degree influenced by the 

 number of vertebrae in that region of the spine to which it belongs. 

 The ganglia are connected by cords of communication, which are 

 not mere nerves, but are true extensions of the ganglia in a cord- 

 like form; so that each lateral chain might be described as a con- 

 tinuous ganglion, with swellings at certain intervals. From each 

 portion certain sets of nerves may be pretty constantly traced : 

 these are, omitting the cords of communication between the ganglia, 

 1. Visceral nerves, which generally accompany branches of neigh- 

 bouring arteries to the viscera. 2. Arterial nerves, apparently 

 devoted to arteries in the vicinity of the ganglia. 3. Nerves of 

 communication with the cerebral or spinal nerves, which emerge 

 from the cranium or spine near to the ganglia. 



The visceral and arterial branches have a remarkable tendency 

 to form plexuses, generally very intricate, which entwine around 

 the blood-vessels, and, in the former case, are conducted by them 

 to the tissue of the viscera. 



The branches of communication with cerebral or spinal nerves, 

 are among the most remarkable connected with this portion of the 

 nervous system. We have already (p. 222, vol. i.) described certain 

 of them as consisting very distinctly of two portions or bundles, one 

 composed of tubular fibres, the other almost exclusively of gela- 

 tinous fibres. These bundles have been very commonly described 

 as constituting the roots of origin of this nerve.f 



On tracing back the gray bundle, connected with one of the 

 spinal nerves, it is found that most of its fibres go to the ganglion 

 of the posterior root of the nerve, some passing into the anterior 

 root. A few of these fibres may be found in each root; they are 

 not, however, traceable into the spinal cord, but seem to connect 

 themselves only with the blood-vessels of that organ. Such is pro- 

 bably the anatomical history of the so called gray root of the sym- 

 pathetic connected with every spinal nerve. It may therefore be 



* See Mr. Swan's beautiful Plates of the Comp. Anat. of the Nervous System. 



t A good figure of these roots is given in Wutzer's work, u De Corporis hu- 

 mani gangliorum fabrica atque usu." Wutzer does not, however, distinguish 

 them as white and gray. Berlin, 1817. 





